CHICAGO (AP) _ McDonald's Corp. announced plans today to introduce a low-fat hamburger to its menus nationwide in response to changing dietary habits.

The McLean Deluxe Burger, which the company says contains 9 percent fat, is scheduled to appear in the chain's 8,800 outlets in the United States by the end of April.

The product responds to customer demands for ''variety, taste and nutrition,'' Ed Rensi, McDonald's president, said in a statement issued by the corporation's headquarters in west surburban Oak Brook.

''McLean Deluxe is a breakthrough for nutrition in America and is an important addition to McDonald's'' menu, Rensi said in a statement.

''It's the right product at the right time,'' he said. ''McLean Deluxe is good news for people who like beef but who want to reduce their fat intake.''

Test marketing began in November in Harrisburg, Pa., and expanded to four more cities in January. The product was tested in 1,000 outlets, said Terry Capatostos, McDonald's public relations director.

The McLean Deluxe contains 310 calories, including condiments, and derives 29 percent of its calories from fat. That compares with 410 calories for the Quarter Pounder, with 44 percent of its calories as fat.

Groups such as the American Heart Association, the National Cancer Institute and the American Dietetic Association recommend that less than 30 percent of the calories consumed in a serving should be from fat.

''People are moving away from red meat,'' said John C. Maxwell Jr., a food and beverage analyst with Wheat First Butcher & Singer in Richmond, Va. ''This is a response to that movement.''

Phil Sokolof, president of the National Heart Savers Association in Omaha, Neb., called the move a ''revolutionary, dramatic breakthrough'' in the way fast food is marketed in the United States.

''This is what we have been striving for,'' he said in a statement. ''This hamburger has the potential to be a major factor in lowering the fat intake of the American people.''

Low-fat burgers have been offered before, but they relied on soy substitute for meat.

Meat in the McLean is made from a new process using carrageenan, a common food additive made from seaweed, The Wall Street Journal reported today. The process devised at Auburn University in Alabama uses carrageenan to bind the beef, allowing water to replace fat.

Analysts say the McLean Deluxe could improve the nutritional image of McDonald's food and start an industry trend.

Michael G. Mueller, an analyst at Montgomery Securities in San Francisco, said the low-fat burger ''would help convince McDonald's customers that the company is in the forefront of health issues.''

It could lead to a whole new menu, just as the Egg McMuffin started a new breakfast trend of muffins and eggs, said George Rosenbaum, president of Leo J. Shapiro & Associates.

But a new lean menu could complicate service at McDonald's, which already has about 50 items, Rosenbaum said.

''They may not be fast-food anymore at this rate,'' he said.